Plasmonic Nano-Objects: From Subwavelength Field Enhancement to Hot Charges and Luminescence

Although bulk gold is known to present very low luminescence quantum yield, gold nanoparticles can present a huge nonlinear luminescence with an apparent high influence of the particle shape. The two-photon luminescence (TPL) of Au nanorods (NR) was investigated at the single-object level, combining polarization-resolved TPL and simultaneously acquired topography using atomic force microscopy (AFM). We evidence that the huge TPL observed in these rods is the result of an interplay between their two different localized surface plasmon resonances. Excitation of gold NR at its longitudinal plasmon frequency first lead to increased absorption and thus increased production of electron-hole pairs that happen to recombine radiatively through the transverse plasmon band i.e. with an enhanced emission at the NR transverse plasmon band. Above fundamental aspects, we show that these specific properties make TPL a highly sensitive technique for the characterization of nanoobjects from their topology to their organization.